fix exec fails for invalid version

libexec/rbenv-exec

@@ -21,7 +21,7 @@ if [ "$1" = "--complete" ]; then
   exec rbenv shims --short
 fi
 
-export RBENV_VERSION="$(rbenv-version-name)"
+RBENV_VERSION="$(rbenv-version-name)"
 RBENV_COMMAND="$1"
 
 if [ -z "$RBENV_COMMAND" ]; then
@@ -29,6 +29,7 @@ if [ -z "$RBENV_COMMAND" ]; then
   exit 1
 fi
 
+export RBENV_VERSION
 RBENV_COMMAND_PATH="$(rbenv-which "$RBENV_COMMAND")"
 RBENV_BIN_PATH="${RBENV_COMMAND_PATH%/*}"
 

test/exec.bats

@@ -9,6 +9,12 @@ create_executable() {
   chmod +x "${bin}/$1"
 }
 
+@test "fails with invalid version" {
+  export RBENV_VERSION="2.0"
+  run rbenv-exec ruby -v
+  assert_failure "rbenv: version \`2.0' is not installed"
+}
+
 @test "supports hook path with spaces" {
   hook_path="${RBENV_TEST_DIR}/custom stuff/rbenv hooks"
   mkdir -p "${hook_path}/exec"